Prestressed concrete members and method of prestressing the same

ABSTRACT

A CONCRETE MEMBER COMPRISED OF A PRECAST CONCRETE MASS WITH AN INNER, IRREGULAR SURFACE OPENING THERETHROUGH, AND HAVING SUBSEQUENTLY A MOLTEN METAL POURED THEREINTO, THE METAL UPON COOLING PROVING A CONTRACTING STRESS TO THE CONCRETE.

l Filed'Nov. 29, 1967 vi.. RAJCHMAN 3,552,074,

PRESTRESSED CONCRETE MEMBERS AND METHODWOF PRESTRESSING THE SAME 2 Sheets-Sheet l INVENTOR. A50/V EA/(//V/l/ z BY, 2y-4J, ZZ'

Jan. 5, 197,1 L. RAJCAMAN 3,552,074

` v PRESTRESSED CNCRETE MEMBERS AND METHOD OF PRESTRESSING THE SAME Filed -Nv. 29, `1967 2 sheets-sheet 2 T .HWWWWWWW INVENTOR. d50/V .FQ/C//M/V United States Patent O 3,552,074 PRESTRESSED CONCRETE MEMBERS AND METHOD OF PRESTRESSING THE SAME Leon Rajchman, 253 W. 73rd St., New York, N.Y. 10023 Filed Nov. 29, 1967, Ser. No. 686,461 Int. Cl. E04c 3/10 U.S. Cl. 52-223 10 Claims ABSTRACT OF THE DISCLOSURE A concrete member comprised of a precast concrete mass with an inner, irregular surfaced opening therethrough, and having subsequently a molten metal poured thereinto, the metal upon cooling providing a contracting stress to the concrete.

BACKGROUND OF THE INVENTION This invention relates generally to self-stressed concrete constructions, and methods for accomplishing the same.

A principal object of the present invention is to provide an improved, self-stressed concrete member and a method for commercial production thereof.

Another object is to provide a prestressed concrete member which incorporates the combination of a metal under contracting stress with a precast concrete mass.

Yet, another object is to provide a prestressed concrete member which incorporates a novel gripping means along a full length between a concrete mass and an elongated metal part whereby the longitudinal stress is maintained throughout the engaging surfaces thereof.

Yet, another object is to provide a novel .prestressed concrete member which, accordingly, would have greater strength for supporting a load in a structure.

Yet, a further object is to provide a prestressed concrete member wherein the linear stressing element may be of steel or other metal or which may be of plastic material.

Yet, a further object is to provide a prestressed concrete member wherein the stressing operation may be performed on a construction job and wherein accordingly the amount of the stressing force can be selectively controlled. f

Other objects are to provide a prestressed concrete member and a method for prestressing the same, which is simple in design, inexpensive in production, easy to use and eicient in operation.

These and other objects will be readily apparent upon a study of the following specification and the accompanying drawings wherein:

FIG. l is a diagrammatical side cross-sectional view of a mold for the present invention showing an initial step in the production method, comprising placement of a pipe across the mold;

FIG. 2 is an enlarged cross-sectional view taken on line 2-2 0f FIG. 1;

FIG. 3 is a view similar to FIG. 1 .and showing a subsequent production step comprising placement of concrete mix into the mold;

FIG. 4 is a side view of the precast member illustrated -partly in cross-section, and showing a subsequent step in Patented Jan. 5, 1971 ly in cross-section, and illustrating a modified design of pipe comprising a part of the present invention;

FIG. 9 is a similar view of another modified design thereof;

FIG. 10 is a similar view of yet another modified design thereof, and

FIG. 11 is a fragmentary perspective view of a further modified design thereof, and

FIGS. 12, 13 and 14 are further designs thereof.

Referring now to the drawings in detail, the reference numeral 10 represents a prestressed concrete member according to the present invention, wherein there is a concrete mass 12, an arcuate pipe 14 extending through the mass 11 and a metal core 16 extending through the pipe 14.

In the present invention, a principal feature is that the core 16 provides a continuously contracting stress to the concrete mass, as indicated by the arrows 18 in FIG. 6, thus giving the same a greater supporting strength. This continuously contracting stress is developed within the .present device by a construction method which is described hereinbelow.

The initial production step comprises the placement of the pipe 14 across a mold 20, as shown in FIG. l. The pipe has a central opening 22, the pipe being externally and internally threaded throughout its length, as indicated by the reference numerals 24 and 26 respectively. The pipe may be made with a longitudinal curvature 28 throughout its length, the curvature being of any predetermined design to suit a particular requirement. The pipe ends 30 are suitably supported and may extend beyond the mold cavity so that no foreign object enters the opening 22 during a following molding operation. The pipe may also be a straight, non-curved pipe.

After the pipe is firmly secured from movement in the mold cavity, a quantity of concrete mix 32 is poured into the mold and around the pipe, as shown in FIG. 3. The concrete is then allowed to set and thoroughly harden which usually requires twenty-eight days. This precast concrete mass 12 with the pipe 14 firmly imbedded therein may then be shipped to a construction site where, as shown in FIG. 4, a molten steel metal or plastic 16a is poured intopthe pipe opening 22. Great carelmust be exercised during the pouring to insure against air pockets being formed. This will assure that the inside Vthreads of the pipe are fully engaged with the molten metal. The pipe is then plugged at both ends. Although the pipe and the concrete member are shown in a vertical position, it should be understo'd that the molten steel or plastic may be poured while both are in any other position.

Next, the assembly is cooled by a spray of cold Water 34, or by any other cooling process. The cooling causes the metal core to contract, however, d-ue to the fact that the pipe threads prevent contraction thereof longitudinally, the molecules of the metal or plastic remain in perpetual contracting stress.

The following formulas and example help to illustrate the principle of this invention when using molten steel or metal:

at-Coef. of expansion e-Strain L Span A-Area E Modulus of elasticity At-Diif temp. P-Force By combining l, 2 and 3 P: Alf@ Amin Therefore (4) P=AMA1E EXAMPLE Find P.

P=AatAtE=2 6.5 lO-GXZOOX 30X 105:78k

It is to be noted that the above formula applies only during the time of elasticity of the metal or steel in particular as determined by Young modulus. As a result At cannot be used as the full differential between 2000 F. instead At is taken at i400 F.

It is to be further noted that the lateral and vertical shrinkage of a steel metal or plastic core is negligible in view of the fact that the cross-sectional dimension thereof is relatively small.

As the steel core cools, the stresses (due to tension) tend to urge the steel to crack; however the action of the concrete on the steel will relieve this tension and prevent the steel core from cracking. This is taken into consideration in the initial design of the member.

As a consequence of the heat transferred from the steel to the concrete during the initial pouring of molten steel, metal or plastic, the concrete may tend to decompose; however, this will be for only a very brief period. As the steel cools, the concrete decomposition will be held to a minimum and will not affect the overall strength of the beam.

In FIGS. 8 to 11, various hollow longitudinal members are shown, each of which includes an internally threaded opening 36. In FIG. 8, the pipe 38 includes spaced apart, integrally formed, external rings 40. In FIG. 9, the pipe 42 has sharp edged corrugations 44, where as in FIG. l0, the pipe 46 has round edged corrugations 48. In FIG. 1l, the pipe 50 has square members 52 integral with the pipe, in spaced apart relation. The rings, corrugations and square members in the above structures each comprise projections for anchoring within the concrete. These hollow longitudinal members may be of steel or other metal alloy or plastic. Some of these materials may melt at lower temperatures than others. Lead, plastic or the like may be employed for pouring and stressing concrete walls in nuclear power plants to restrain radioactivity and in building foundations for the same purpose. Furthermore, the stressing means itself need not be prestressed, as has been the practice heretofore.

While various changes may be made in the detail of the method in construction; it is understood that such changes will be within the spirit and scope of the present invention as dened by the appended claims.

Having thus disclosed the above invention, what I claim and desire to secure by Letters Patent of the United States of America is:

1. In a depressed concrete member, the combination of a precast concrete mass, a hollow member through said concrete mass, and a subsequently poured molten metal within said hollow member forming a contracting stress means for said concrete.

2. The combination as set forth in claim 1, wherein said hollow member comprises an elongated pipe that is internally threaded throughout its length, the external side of said hollow member having projections for engaging said concrete mass.

3. The combination as set forth in claim 2, wherein said hollow member is longitudinally curved.

4. The combination as set forth in claim 3, wherein said external projections comprise an external thread throughout the length of said hollow member.

5. The method of stressing concrete members comprising the steps of providing a form for receiving concrete, forming an hollow longitudinal member with spaced projections on its inner and outer walls, positioning the member in the form, pouring concrete into the form to a desired level to encase the member, allowing the concrete to harden, pouring into the hollow member heat-expansible substance at said substances melting temperature, closing the ends of the hollow member and allowing the concrete member, the hollow member and the substance therein to cool to room temperature.

6. The method according to claim 5, wherein the hollow member is formed as a steel pipe and the projections are formed as internal and external spiral threads on said pipe, the heat expansible substance being metal heated to a melting temperature.

7. The method according to claim 5, wherein said hollow member is formed of plastic material, said heat-expansible substance plastic material.

8. The method according to claim 5, wherein the internal projections in said member are formed as spiral threads, the external projections being formed as spaced, integrally formed rings.

9. The method according to claim 5, wherein the internal projections in said member are formed as spiral threads, the external projections being formed as integral round corrugations.

10. The method according to claim S, wherein the internal projections in said hollow member are formed as spiral threads, the external projection being formed as integral square members.

References Cited UNITED STATES PATENTS 1,770,932 7/1930 Leake 52-225X 2,921,463 1/1960 Goldfen 52-223 2,963,273 12/1960 Lane 52-223X 3,060,640 10/1962 Harris 52-230 3,167,882 2/1965 Abbott 264-228X 3,202,740 8/1965 Patin 264-228 3,217,075 11/1965 Kjell-Berger 52-223X 3,290,840 12/1966 Middendorf 52-223 FOREIGN PATENTS 710,718 6/1965 Canada.

ALFRED C. PERHAM, Primary Examiner.

U.S. Cl. X.R. 264-228 

